My first year of growing sweet potatoes was also my worst sweet potato harvest year ever. They were so small and I harvested very few. Thank goodness for learning from mistakes. I’ve been consistently growing massive sweet potatoes every year since. I made 7 changes to the way I grew them the first year and it really paid off. I would guess (someone test it and tell me!) you may even be able to harvest big sweet potatoes in the northern US where they are harder to grow, using these secrets!